Originally Posted by
Andrew R Stewart
The classic chain length determining is to place the chain in the big/big and add 1 or 2 link pairs. I've always tended to go longer if all works well, as you can always shorten the chain easily, if needed. Actual length is a factor of cog/ring size, der, cage design, pulley wheel size, hanger length, chain stay length AND the rider's ability to stay out of cog combos as needed. Andy.
+1.5
I would emphasize that the chain needs to be long enough to go around the big cog and big chainring, with enough slack to allow the rear derailleur to shift into this combination. A too-short chain can cause the the derailleur to jam (at least) or tear it completely off the bike (at most). A chain that's too long will hang slack in the little-little combination. Embarrassing, but not a real problem.